Alpha-numeric display system



P. M. CROSNO ETAL ALPHA-NUMERIC DISPLAY `SYSTEM Nov. 24, 1964 3 Sheets-Sheet 1 Filed Nov. 28. 1960 .wljmo OPOIa Nov. 24, 1964 P. M. cRosNo ETAL 3,153,857

ALPHA-NUMERIC DISPLAY SYSTEM Filed Nov. 28. 1960 3 Sheets-Sheet 2 AMPLITUDE DRIVEN BY ANTENNA INVENTORS. PHILIP M. CROSNO.

FRANK wEmG JR. Ig lg M ?'w ATTORNEYS.

Nov. 24, 1964A p, M, cRosNo ETAL 3,158,857

ALPHA-NUMERIC DISPLAY SYSTEM 3 Sheets-Sheet 3 Filed Nov.. 28. 1960 v 1 I I I I I I I I I I I INVENToRs. PHILIP M. CROSNO. BY FRANK L. wEDlG JR.

m Q, W? 6 A oRNEYs.

United St'ates Patent 3,158,857 ALPHA-NUMERIC DISPLAY SYSTEM Philip M. Creane and Frank L. Wedig, Jr., Cincinnati, hio, assignors to Aveo Corporation, Cincinnati, (Ehio, a corporation of Delaware Filed Nov. 28, 19%, Ser. No. 72,056 19 Claims.. (Cl. 343--5 This invention relates to a system of direct labeling of data display information presented on a cathode-ray oscilloscope and, more particularly, to the novel means for the display of established symbols simultaneously with the related data on a cathode-ray tube oscilloscope, the symbols being maintained throughout in constant size, aspect, and rectitude.

Direct labeling of data display information is becoming more essential as system complications increase and resolution time decreases. For example, in an air traffic control radar system for which the present invention .was conceived, the simultaneous presentation on a PPI scope of as many as twenty-four airplanes was required. Since the airplanes are constantly changing position, it would be virtually impossible for an operator to keep track of each airplane without some system of identification. By means of this invention, the return signal indication from each airplane is marked by an identifying symbol which constantly follows the indication as it moves about the cathode-ray tube screen; and the symbol is maintained in constant size, aspect, and rectitude.

There are many prior art devices capable of applyingl an appropriate symbol Vto a cathode-ray oscilloscope. These include complex function generators and charactrons. Although these work fairly well, they areV very complex, resulting in high cost and dillicult and expensive installation and maintenance. system simplification which results in a considerable reduction in cost and an increase in reliability.

The primary object of this invention is to present established identifying symbols, alpha-numeric or line drawing, adjacent related data indications on a cathode-ray tube.

Another object of this invention is 'topresent established identifying symbols adjacent related data indications on a PPI display and to maintain the symbols at a constant size and rectitude. A,

Another object of this invention is to present symbols on a PPI scope at a position corresponding to the azimuth and range of a selected target.

Still another object of this invention is to rectilinearly scan a symbol with a beam of light to produce electrical impulses which are applied to the intensity control grid of a PPI oscilloscope, the scanning of the symbol in one direction being synchronized'with the radial sweep of the beam of the oscilloscope, said scan being controlled to originate at determined periods, and thereby reproduce the symbol on the oscilloscope. i

Another object of this invention is to present on a PPI radar cathode-ray tube identifying symbols adjacent a preselected target by applying, at controlled times to the intensity control grid of the oscilloscope, voltages produced by scanning said symbol with a beam of light in two dimensions, the sweep of said beam in one dimension being in synchronism with the radial sweep of the beam of the cathode-ray tube.

A further object of this invention is to present on a PPI radar cathode-ray tube identifying symbols adjacent a preselected target by applying, at controlled times to the intensity control grid of the oscilloscope, voltages produced by scanning said symbol with a beam of light in two dimensions, the sweep of said beam in one dimension being in synchronism with the radial sweep of the This invention provides n Patented Nov. 24, 1964 beam of the cathode-ray tube, and rotating the scan of the symbol counter to the PPI sweep in synchronism therewith. Y f

Still another object of this invention is to provide a Vsymbol display system in which symbol size is constant, irrespective of the position of the symbol on the cathoderay tube.

Another object of this invention is to provide a unique generator capable of producing sawtooth oscillations having constant maximum and minimum values, irrespective of the slope.`

For further objects and for a more complete understanding of the operation of this invention, reference should now be made to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation, partly in Vtratiic control system inwhich the invention was actually reduced to practice. The over-all air traffic control system, which utilizes PPI radar apparatus, is vcapable of automatically tracking, scheduling, and issuing orders for controlling the altitude and heading of aircraft so that they will arrive at selected intervals at the entry point of a landing system (G.C.A., I.L.S., etc.) in line with the runway and at a proper altitude. Since the entire air traffic control system is very complex and is not required for an understanding of the present invention, only those portions required to present an environment for this invention will be described. In the particular system, as many as twenty-four aircraft are simultaneous'- ly handled and displayed on a single PPI scope. This invention provides the appropriate labeling of each aircraft displayed. Y

The air traffic control system incorporating this invention is illustrated in part in block diagram in FIG., 1, where there is shown a conventional PPI radar display including a cathode-ray tube 19 used for presenting indications in polar coordinates of reflected target returns from controlled aircraft. lIt is to be understood, of course, that any other data may also be presented, and this invention is not limited to aircraft. For example, the data may be a particular item on an assembly line, or trains in a large switching yard. The beam of the cathode-ray tube 10 is swept by conventional means angularly in synchronism with the radar antenna, and radially by a sawtooth voltage representing a predetermined range.

` Conveniently, the beam may be swept in azimuth by a conventional annular yoke 11 rotated in synchronism on the axis of the cathode-ray tube 10 through a gear 13 driven by the antenna. The range deflection is provided by the sawtooth output applied to the yoke 11 from a conventional range tirner l5, the operation of which is initiated by the usual range trigger. The intensity of the beam is controlled by the target return signals applied to the control grid 14 from the radar receiver (not shown) to produce a plurality of data indications 12, i.e., indications of the aircraft targets.

The control grid 14'.- of the cathode-ray tube 10 is also controlled by the output from light-sensitive photoelectric cell 16 which, as will be seen, yields an alpha,- numeric symbol and presents each symbol on the screen adjacent a particular data indication 12. lt will be understood that the apparatus illustrated produces only the symbol A3 and that other essentially duplicate apparatus is required for producing the other illustrated symbols A1, A2, and A4.

`The system for producing the alpha-numeric display symbol A3 comprises a conventional flying spot scanner which includes a cathode-ray tube 18 having a phosphorescent screen 2d, a cathode 22, horizontal deflection plates 24, and vertical deflection plates 26. TheA beam .of the cathode-ray tube i8 is swept rectilinearly, in a manner to be described, across the phosphorescent screen 20, and the beam of light which is produced on the screen 2,0 passes through a symbol mask 28. Preferably, the symbol mask 28 may consist of appropriate alpha-numeric or line drawings which are transparent in an opaque eld and, for example, may take the form of a conventional photographic plate negative. The mask 28 is positioned between the flying spot scanner cathode-ray tube i3 and the photoelectric cell 16 to convert the transparent areas of the mask into electrical impulses. The electric impulses from the photocell are, in turn, used to control the intensity of the beam of the cathode-ray tube 10.

For the purpose of providing the rectilinear sweep for the beam of the flying spot scanner cathode-ray tube i8, the air trailc control system in which this invention was incorporated included a tracker for each aircraft under control. Each tracker provided the function of tracking1 a selected target and was provided with an electronic early-late gate which permitted the particular tracking unit to respond only to the selected target within a predetermined set of polar coordinates; and each tracker functioned to continuously report the changing position of the target in terms of direct voltages representing range and azimuth. That is to say, the tracker, in so far as this invention is concerned, serves the function of providing two voltages, one representing the instantaneous azimuth V and the other representing the instantaneous range VR of the tracked aircraft. The details of the tracker form no part of this invention and, therefore, are not included in this description; and the tracker 30 illustrated simply in block form is represented as having a direct voltage output VR representing range and Vo representing azimuth.

The voltages VR and V, are compared in magnitude with the sawtooth voltages VR(ref) and V0(ref) generated in Range and Azimuth sawtooth voltage generators 32 and 34, respectively. The sawtooth output from the range reference voltage generator 32 is initiated by the range trigger. The voltages VR(ref) and `V(ref) are synchronized with the deection voltages of the cath ode-ray tube 10. rl`hat is to say, the range reference sawtooth voltage VR(ref) represents lthe range coordinate, while the azimuth reference sawitooth voltage V(ref) represents the angular coordinate of the beam on the screen of the cathode-ray tube 10. The system is designed so that when the beam of the cathode-ray tube i@ is in coincidence with the appropriate data indication i2, i.e., the indication adjacent symbol A3, the instantaneous values of voltages V0(ref) and VR(ref), respectively, equal the direct voltage outputs VR and V, from the tracker 30. For the purpose of determining when this instant of equality occurs, the voltages VR and VR(ref) are compared in a range comparator 36, a voltage spike 37 being produced in the output of the range comparator 36 when the voltages are equal. The voltage spike 37 is then applied to a range scanner trace generator 3S. Similarly, the voltages VD and V0(ref) are compared in an azimuth comparator 46, a voltage spike 41 being produced and applied to an azimuth scanner trace generator 4-2. when equality exists.

The scanner trace generators 38 and 42 are described hereinafter in more detail. However, it should be noted at this point that upon the occurrence of a voltage spike 41 at the input of the azimuth scanner trace generator 42, a sawtooth voltage 44 and a square Wave voltage 46 are simultaneously produced at first and second output leads 45 and 47, respectively. When the voltage spike 37 is presented at one input of the range scanner trace generator 33 and also when the square wave voltage 46 is simultaneously applied at a second input, a sawtooth voltage d and a square wave voltage 5t) are produced at output leads 49 and 5l, respectively. Note that the range scanner trace generator 38 is so arranged that the occurrence of a voltage spike 37 will not render it operative in the absence of the square wave voltage i6 from the generator 42, an event which occurs only when there is coincidence in the azimuth coordinate. Thus, both generators 38 and 42 are rendered operative only upon the coincidence in both the azimuth and range coordinates.

The sawtooth output 44 of the azimuth scanner trace generator 42 is applied to the amplifier and phase splitter 54- and then to the vertical deflection plates 26 of the cathode-ray tube 10 to drive the beam vertically. Simultaneously, the square wave output de is applied Ito the generator 33 to start its operation. The square wave output 5b of generator 3S is then applied to the intensity control grid 23 of the cathode-ray tube 1S to brighten the beam of the tube. In addition, the sawtooth voltage 4S is applied to the amplifier and phase splitter 52 and to the horizontal deflection plates 2d of the cathode-ray tube to delect the now-brightened beam horizontally.

Since the range reference voltage VR(ref) is in synchronism with the range sweep of the beam of the cathode-ray tube it), it is apparent that a voltage spike 37 will result each time the voltage VR equals VR(ref), and that during the period that the square wave i6 is applied, a sawtooth voltage 4S will be repeatedly generated. Thus, for the duration of the square wave 4d, the beam of the cathode-ray tube i8 will be honizontally swept each -time the beam of the cathode-ray tube i@ is swept radially.

Thus, a rectilinear television type scan of the beam of the cathode-ray tube 1S is produced across .the phosphorescent screen 20 immediately after each occurrrence of coincidence of the beam of the cathode-ray tube 10 with the target return indication. Since the light produced on the phosphorescent screen 2t) passes through the alpha-numeric mask 21S, the photocell 16 is energized by light energy representing the particular alphanumeric symbol A3, and this energy is synchronized with the range sweep of the cathode-ray tube i0. When the voltage output from the photocell 16 is applied to the intensity control grid 14 of the cathode-ray tube 10, the alpha-numeric symbol is presented on the screen of the cathode-ray tube it) positioned immediately radially beyond the particular data indications i2 representing the selected target being tracked by the tracker 30.

With a system constructed as thus far described, there are two undesirable conditions resulting which require correction; namely, the size of the symbols will change, depending on the distance of the data indication 12 from the center of the cathode-ray tube; and, further, with the mask 2S `in a fixed position the alpha-numeric display will not be in constant rectitude. That is to say, if the alpha-numeric symbols are upright in one position on the screen of the cathode-ray tube 1G, then they will be upside down when the target moves degrees from that position.

The symbol size will not be constant without additional circuitry because of the nature of a PPI radar display. That is to say, in a PPI display the origin of the cathoderay tube sweep represents the geographical location of the radar antenna, and the beam is then swept both radially'and angularly. The radial sweep to the outer extremity of the cathode-ray tube yis at a linear rate, and it provides a linear relationship between range and time,

FIG. 2 illustrates the manner in which the symbol size will change without additional corrective circuitry. Re-

membering that the radial length 1 of any symbol isv determined by the duration of the horizontal Vsweep applied to the beam of the cathode-ray tube 18, it will be seen that the dimension 1 is a function of the magnitude of the sawtooth wave 48. In the description below of the scanner trace generator 38, it will be shown that the magnitude of the sawtooth Wave 4S is maintained constant, regardless of its duration. Therefore, the dimension 1 is maintained constant. It will also be recalled that the arcuate height h of the symbol area is determined by the duration of the sawtooth wave 44 and by the angular sweep of the beam of the cathode-ray tube 10. If the duration of the sawtooth wave 44 is maintained constant, then for any given angular sweep a point on the beam at a range R1 will travel a greater distance h1 than a point on the beam at a shorter range R2 where only a distance 112 is traversed. Thus, as may be seen by a comparison of the solid line symbol at range R1 and the dotted line symbol at range R2, a change in size of the height dimension h Will occur proportional to the range R of the target from the radar antenna, and this dimensional change in the symbol causes a serious aspect ratio (1/ h) distortion for any symbol information.

, In order to maintain a constant aspect ratio While simultaneously maintaining a constant size, the dimension h is made to vary inversely with range, and for this purpose we provide a-symbol aspect ratio correction circuit 56 which will be described in detail below. As will be seen, the duration of the sawtooth voltage output 44 is adjusted in accordance with range (VR) to provide a reduced duration verticalsweep for the cathode-ray tube 18 as lthe voltage VR increases and an increased duration when VR decreases. This results in a symbol presentation which will have a constant height h.

Because of the rotation of the beam of the PPI display, the symbols illustrated in FIG. l2 are not in proper rectitude, and it will be understood that proper rectitude can be established at only one target azimuth, namely, due east. Tocorrect for this misalignment the symbol mask 28 is properly oriented for av given position and is then rotated synchronously with the radar antenna through gearing 60 in a direction counter to that of the PPI sweep rotation, or if more practical, the mask 2S may be driven by a servo motor synchronized with the rotation of the radar antenna by conventional servo practices.

The details of the scanner trace generators 33 and 42 and the symbol aspect ratio correction circuit 56 are shown in FIG. 3, to which reference is now made. It will be recalled that two outputs are required from each of the generators 38 and 42, one a square wave and the other a sawtooth wave. To produce .these outputs we provide two essentially identical circuits differing pri-v marily in parameters to stants required. y

The range scanner trace generator 38 comprises a triode V1 having a plate 61, a grid 62, and a cathode 64, and a triode V2 having a plate 66, a grid 68,V and a cathode 70. The cathodes 64 and 70 are connected directly to ground while the plates 61 and 66 are connected to a B-lsupply through plate resistors 72 and 73, respectively. The plate 61 of triode V1 is connected to the grid 68 of triode V2 through condenser 74, and the plate 66 of triode V2 is connected to the grid 62 of triode V1 through parallel-connected condenser 76 and resistor 78. The grid 62 is connected to a B- supply through a resistor 80. A diode 82 is connected between the grid 68 and ground. The condenser 74 is connected to a xed direct current B-lsupply through a variable resistor 84 and a provide the different time confixed resistor 86. The grid 68 of triode V2 is connected to the output lead `47 of the azimuth scanner trace generator 42 through a clamping diode 88. The square wave output 5t) for brightening the beam of the cathode-ray tube 13 is derived from the plate 66 through a condenser 87. Input voltage spikes 37 are applied to the circuit through a diode 89.

The azimuth scanner trace generator 42 is essentially identical to that of the range scanner trace generator 38, and it comprises a triode V3 having a plate 90, a grid 92, and a cathode 94, and a triode V4 having a plate 96, a grid 98, and a cathode 100. The cathodes 94 and 100 are connected directly to ground while the plates and 96 are connected to the B+ supply through plate resistors 102 and 103, respectively. The plate 96 of triode V3 is connected to the grid 98 of triode V4 through a condenser 164, and the plate 96 of triode V4 is connected to the grid 92 of the triode V3 through parallel-connected condenser 196 and resistor 108, the grid 92 also being connected to a B- supply through a resistor 110. A diode 112 is connected between the grid 98 and ground. The condenser 104 is connected to a large direct current supply through variable resistor 114 and fixed resistors 116 and 132. Unlike the generator 3S, this direct voltage is automatically variable and is derived from the output lead 117 of the symbol aspect ratio correction circuit 56. Input voltage spikes 41 are coupled to the circuit from the range comparator through a diode 119.

Discussing first the operation of the azimuth scanner generator 42, initially (at time to, FIG. 4) the triode V4 is maintained at maximum conduction by the clamping of the grid 98 to ground potential by means of the diode 112. This results in a low voltage at the plate 96, and this voltage is not sufficient to overcome the cutoff bias from the B- supply applied to the grid 92 of the triode V2. Y Therefore, the sawtooth voltage output 44 at lead 45 is maintained at zero and the square Wave voltage output 46 at lead 47 is maintained at a negative level equal to the cutoff voltage applied to the grid 92.

Upon the occurrence of the negative voltage spike 41, the condenser 164 is charged through the diode 119, and the triode V4, is rendered momentarily non-conductive. This results in a sudden increase of the voltage at the grid 92 of triode V2, thereby driving that triode into conduction. Conduction of triode V2 results in the application of a decreased voltage from the plate 9% to the grid 98 of the triode V4, which is thereby driven into cutoff. When V4 is cut off, V3 is at maximum conduction, i.e., drawing grid current. Thus at t1 the square wave Voltage 46 at lead 47 is suddenly raised from `a negative voltage to zero, and the sawtooth voltage 44 at lead 45 is reduced to cutoff grid bias potential of triode V4 at a rate determined by the rate of discharge of condenser 104.

The charge on condenser 104 leaks oh? at a rate dependent on the time constants of condenser 164 and resistors 114 and 116 and on the magnitude of the voltage from the aspect ratio correction circuit 56. If resistors 114 and 116 are held fixed, this results in an output from lead 45 which is a sawtooth voltage having a duration dependent upon the voltage supplied from the aspect ratio correction circuit 56. When the charge leaks off condenser 104 at time t2, the triode V4 returns to maximum conduction, and the triode V3 is returned to cutoff. Thus, the output voltage on lead 47 is a square wave having an initial negative value and then, for a period of time t1 to r2 has a zero potential. The parameters are designed so v that the negative value of the square Wave 46 is sufiicient to maintain the triode V2 in the generator 38 at cutoff under all operating conditions.

Referring now to the scanner trace generator 38, it will be seen that at time to the negative Voltage applied through the lead 47 and the diode 88 to the grid 68 maintains triode V2 at cutoff. The large resultant voltage on the plate 66 is applied to the grid 62 and is sufficient to overcome the negative cutoff bias applied from the B- supply. Therefore, triode V1 is initially in maximum conduction, that is, drawing grid current, while triode V2 is maintained in cutoff.

Since the cutoff bias provided at lead 47 through the diode Sti is suiiicient to maintain the triode V2 cutoff at all times, receipt of a voltage spike 37 will not change the status of the triodes until this bias is removed. Upon removal of the cutoif bias from the grid 63, the triode V2 is rendered conductive and the triode V1 is cut off. Operation then results in a manner similar to that of the generator 42, that is, receipt of voltage spikes 37 will cause the triodes to change state. The voltage charge developed across condenser 74 by a subsequent voltage spike 37 leaks off through resistors Sli and Sd and, hence, a sawtooth voltage 48 is produced at the output lead 49 having a duration fixed by the circuit time constants. It will be noted that the maximum and minimum values of the sawtooth wave will be fixed, irrespective of the duration of the wave. This is because the maximum and minimum values are determined by the voltages on the grid 63 of triode V2 when it is cut off, and again when it is at maximum conduction. Since these two values are predetermined by tube characteristics and circuit design, the sawtooth voltage will have a constant amplitude and, hence, the length 1 of the displayed symbol will be maintained constant on the screen of the cathode-ray tube.

In order to maintain the height dimension l1 of the symbol constant, the duration of the sawtooth wave i4 applied to the deflection plates 24 is varied in inverse proportion to the voltage VR. This is accomplished by the aspect ratio correction circuit 55 which provides a variable voltage for one plate of the condenser 1%.'

The circuit 56 includes a first triode V5 having a plate 122 connected to a B+ supply, a grid 12d connected to the VR output of the tracker 3b, and a cathode 126 connected to ground through a cathode resistor 123. A second triode V5 having a plate 13d connected to the i3-1- supply through a resistor 132 and a grounded grid 134 is provided with a variable voltage directly proportional to VR at its cathode 136 from cathode resistor 128 through a movable tap 138. In operation of the correction circuit 56, an increasing voltage VR applied to the grid 124 produces increased conduction through the triode V5 and, therefore, develops an increased voltage across the resistor 123 and on the cathode 136 of triode V6. The increased voltage which results on the plate 13G is applied through the lead 117 to one plate of the condenser lil-t in the azimuth scanner trace generator 42.

Since the duration of the sawtooth wave 44 is a function of the RC. time constants and the voltage difference between the plates of the condenser 104, it is evident that the duration of the sawtooth wave will be a function of the voltage E on one plate, if the voltage on the other plate is maintained constant. Mathematically, this relationship is defined as T=ln E, where T is the duration of sawtooth wave 44 and E is the voltage at lead 117. Since at small angles the natural logs (1n) are approximately equal to tangents, then referring to FIG. 4, l1, which is a function of 9, may be varied in accordance with the equation: ln E=tan1h/R0. It is clear, therefore, that an increase in the value of VR will decrease the length of the sawtooth wave, thereby maintaining the dimension h of the symbol constant.

While in most instances the mask 28 illustrated in FIG. 1 may be adequate for identification of the particular data, in some applications it may be desirable to use a mask such as illustrated in FIG. 5. This mask is cornprised of two portions consisting of a disk 150 and a tangentially positioned plate 152, both the disk and the plate having translucent symbols on an opaque background.

In the particular embodiment illustrated in FIG. 5, the symbols on the plate 152, in conjunction with the numerals on the rotatable disk 15G, are extremely useful in an air traffic control system. For example, the symbols on the plate 152 might be used to designate the particular target, and whether or not the target is late, early, or on g' time. That is to say, the symbol A might identify the aircraft while AE and AL give early and late indications. The numerals on the disk might indicate altitude or range.

The point of contact between the disk 151i and the plate 152 is positioned in front of a cathode-ray tube 154A similar to the tube 18 in FIG. 2. In this embodiment, however, the cathode-ray tube is mounted in a gear 156, and the entire tube 154 is rotated on its axis by a drive connection from the radar antenna through gearing 153. This rotation is counter to the rotation of the PPI scope azimuth scan and serves the purpose of maintaining proper rectitude of the symbol. The mask 152 may be driven by an appropriate servo motor so as to position the appropriate on-time early or late symbol (A, AE or AL) at the point of contact; and similarly, the mask 152 may be driven by another servo motor in response to the range, altitude, or other information relative to the target. The light passing through the mask is directed toward the photocell 16.

Having thus described this invention, what is claimed is:

l. 1n a cathode-ray tube display system wherein a data indication is presented on the screen of a cathode-ray display tube by brghtening the beam of said tube at a controlled time, said beam being deiiected radially at a high rate and angularly ata relatively low rate, and means are provided for presenting a symbol on said screen adjacent said data indication for identifying said data indication, the combination comprising: a light sensitive device for producing a voltage output in response to light energy, said Voltage output being coupled to said cathode-ray display tube to control the brightness of the beam of said tube; a cathode-ray scanner tube having a phosphorescent screen and horizontal and vertical deflection means; a mask comprised of opaque and translucent portions having a pattern representing said symbol, said mask being interposed between the screen of said cathode-ray scanner tube and said light sensitive device; means for relatively rotating said mask and said screen in synchronism with said angular deflection in the direction counter thereto; means for rectilinearly sweeping the beam of said cathode-ray scanner tube across said mask, said means including a first generator having a first sawtooth voltage output coupled to one of said deflection means, and a second generator having a second sawtooth voltage output coupled to the other of said deflecting means, said second sawtooth voltage output being synchronized with the radial deflection of the beam of said cathode-ray display tube in one dimension; and means for initiating operation of said generators at said controlled time whereby said beam of said display tube is brightened in accordance with said pattern and said symbol is presented on the screen of said cathode-ray display tube adjacent said indication.

2. The invention as defined in claim l, wherein means are provided for regulating the duration of the sav/tooth voltage output of said first generator in inverse proportion to the radial distance of said data indication from the origin of the beam on the screen of said cathode ray display tube.

3. The invention as defined in claim 2 wherein said second generator is rendered inoperative except for the period of duration of said sawtooth voltage of said first generator.

4. In a radar system for presenting a reflected target signal as an indication on the screen of a PPI cathode ray display tube, said tube having beam defiection means and beam brightening means, said beam being deflected radially at a hifvh rate and angularly at a relatively low rate, the radial deflection being a function of range, and the angular deection being a function of azimuth, and means for presenting an identification symbol on said screen adjacent said indication, the combination comprising: means for producing a rst direct voltage which is a function of the range of said target; a range reference voltage source for generating a first sawtooth voltage hav- 9 ing a magnitude which is a function of range; means for comparing said first direct Voltage with said first sawtooth voltage and for producing a range coincidence pulse when said voltages are equal; means for producing a second direct voltage which is a function of the, azimuth of said target; an azimuth reference voltage source for generating a second sawtooth voltage having a magnitude which is a function of azimuth; means for comparing said second direct voltage with said second sawtooth voltage for producing an azimuth` coincidence pulse when said second direct voltage and said second sawtooth voltage are equal;

`a iiying spotv scanner comprising a cathode rayV scanner tube having a phosphorescent screen, horizontal and vertical deflection plates, a range scanner trace generator for generating a sawtooth voltage output for energizing said horizontal deiiection plates for horizontally deiiecting the beam of said scanner tube, an azimuth scanner trace generator for generating a sawtooth voltage output for energizing said vertical deection plates for vertically deiiecting the beam of said scanner tube, operation of said range and azimuth scanner trace generators being initiated by said range and azimuth coincidence pulses respectively, said range scanner trace generator being biased for nonoperation except for the period of duration of the sawtooth voltage output of said azimuth scanner trace generator; a light sensitive device; a mask interposed between the screen of said scanner tube and said device, said mask comprising opaque and translucent portions having a pattern representing said symbol, the output from said light sensitive device being coupled to said beam brightening means of said display tube, the radial deflection of the beam of said display tube being synchronized with the sawtooth voltage of said range reference voltage.

5. The invention as defined in claim 4 wherein the duration of each sawtooth voltage wave generated by said azimuth scanner trace generator varies in inverse proportion to the range of said target, whereby the arcuate length of said symbol is maintained constant.

6. The invention as defined in claim 5 wherein the minimum and maximum magnitude of the sawtooth voltage generated by said range scanner trace generator is maintained constant, whereby the radial length of said symbol is maintained constant.

7. The invention as defined in claim 4 wherein said mask and said scanner tube are relatively rotated in synchronism with the angular deflection of the beam of said display tube in a resultant direction counter thereto.

8. The invention as defined in claim 4 wherein said mask comprises a disk rotatable on an axis, and a plate tangentially movable at the periphery of said disk, the point of contact of said plate and disk being positioned in the path of said beam of light between said screen and said device, the patterns of said plate and disk representing a plurality of symbols which may be selectively positioned in said path.

9. A sawtooth generator comprising: first and second triodes each having a plate, a grid, and a cathode, said cathodes being connected to a point of reference potential and each of said plates being connected to a source of direct voltage through a plate resistor; a connection from the plate of said first triode to the grid of said second triode through a first condenser; a connection from the plate of said second triode to the grid of said first triode through a second condenser; a leakage path for said lirst condenser connected from a point of positive potential to the junction of said first condenser and the grid of said second triode; a diode connecting the grid of said second triode to said point of reference potential, said diode being poled for conduction from the grid of said second triode to said point of reference potential, and avsource of nega-V tive cut-olf potential applied to the grid of said iirst triode through a resistor, whereby said second triode is at maximum conduction and said first triode is cut ofi; means applying a voltage pulse to the plate of said first triode to render said rst triode conductive at a maximum level and to cut ofi said second triode; and means for deriving a sawtooth output voltage from said junction, the magnitude of said sawtooth voltage output being constant between limits determined by the grid voltage of said second triode at maximum conduction and at cut-oli.

l0. The invention as defined in claim 9 wherein said point of positive potential is `automatically variable in accordance with a function, and the duration of said sawtooth voltage output is variable in inverse proportion to the voltage at said point of positive potential.

l1. In a cathode-ray tube display system wherein a data indication is presented on the screen of a cathoderay display tube by brightening the beam of said tube at a controlled time, vsaid beam being defiected at a high rate in one dimension and at a relatively low rate in a second dimension, and means are provided for presenting a symbol on said screen adjacent said data indication for identitying said data indication, the combination comprising: a light sensitive device Vfor producing a voltage output in response to light energy, said voltage output being coupled to said cathode-ray display tube to control vthe brightness of the beam of said tube; a cathode-ray scanner tube having a phosphorescent screen and horizontal and vertical deflection means; a mask comprised of opaque and translucent portions having a pattern representing said symbol, said mask being interposed between the screen of said cathode-ray scanner tube and said light sensitive device, said mask comprising a disk rotatable on an axis, and a plate tangentially movable at the periphery of said disk, the point of contactof said plate and disk being'positioned inthe path of said beam of light between said screen and said device, the patterns of said plate and disk representing a plurality of symbols which may be selectively positioned in said path; means for rectilinearly sweeping the beam of said cathode-ray scanner tube across said mask, said means including a iirst generator having a first sawtooth voltage `output coupled to one of said deflection Vmeans, and -a second generator having a second sawtooth Vray display tube in one dimension; and means for initiating operation of said generators at said controlled time whereby said beam of said display tube is brightened in accordance with said pattern and said symbol is presented on the screen Vof said cathode-ray tube display adjacent said indication. V v

l2. The combination comprising: a cathode-ray display tube having a phosphorescent screen, deection means for sweeping the beam of said cathode-ray display tube over said screen in two dimensions, said dimensions being radial and angular, and intensity control means for said beam; la beam of radiant energy; a radiant energy sensitive device for producing an output responsive to the intensity of said beam of radiant energy intercepted thereby, said output being applied to said intensity control means of said cathode-ray display tube; a medium having a radiation transmission characteristic pattern, said pattern representing a symbol, said medium being interposed between said beam of radiant energy and said radiant energy sensitive device; first means for sweeping said beam of radiant energy over said medium in one dimension; second means for sweeping said beam of radiant energy over said medium in a second dimension, the sweeping of said beam of radiant energy in one dimension being synchronized with the radial sweeping of the beam of said cathode-ray display tube; means for initiating the sweep -of said beam of radiant energy over said medium at selected times; and means for relatively rotating the orientation of the sweep of said beam of radiant energy with respect to said medium in a direction opposite to the angular sweep of the beam of said cathode-ray display tube.

13. The invention as defined in claim 12 wherein said first means for sweeping said beam of radiant energy is l 1 inoperative except when said second means for sweeping said beam of radiant energy is operative.

14. The invention as defined in claim 12 wherein said means for relatively rotating said orientation comprises means for mechanically rotating said medium in a direction opposite `to the angular sweeping of the beam of said cathode-ray display tube.

15. In a system for displaying the plan position of a moving target in radial and angular coordinates, said system including a cathode-ray display tube, the beam of which is deflected radially at a relatively high rate as a function of range and angularly at a relatively slow rate as a function of azimuth, and modulating means for modulating said beam to produce a moving indication of the position of said target in said coordinates on the screen of said display tube, the combination including means for superimposing a symbol on said screen continuously adjacent said moving indication, said means for superimposing a symbol comprising: a beam of radian-t energy; a radiant energy sensitive device for developing an output voltage in response to radiant energy intercepted thereby, said output voltage being coupled to said modulating means for further modulating said beam of said display tube; a medium having a radiation transmission characteristic pattern, said pattern representing a symbol, said medium being interposed between said beam of radiant energy and said radiant energy sensitive device; means for scanning said medium with said beam of radiant energy to sensitize said device in accordance with the scanned pattern of said medium, saidscanning means including first and second generators for generating first and second deection voltages for detlec-ting said beam of radiant energy in irst and second coordinates, said first generator being synchronized with the radial deflection of said display tube; means responsive to coincidence of the beam of said display tube with the angular positioned coordinate of said target indication for rendering said second generator operative for generating said second deflection voltage `for deiiecting said beam of radiant energy in said second coordinate; and means responsive to the coincidence of the beam of said display tube with the radial position coordinate of said target indication and to the generation of said second deflection voltage for successively rendering said first generator operative to successively generate said iirst deflection voltage for deileoting said beam of radiant energy in said one coordinate, said rst generator being inoperative in the absence of said second deection voltage output from said second generator, whereby the beam of said display tube is modulated in accordance with said pattern and said symbol is superimposed on said display tube at a position continuously adjacent said target indication.

16. The invention as dened in claim l5, and means for relatively rotating the orientation of the deflection of said beam of radiant energy withL respect to said medium in a direction opposite to the angular deflection of the beam 12 of said display tube, whereby said symbol is maintained in proper rectitude.

17. The invention as dened in claim 16 wherein said first and second coordinates are rectilinear.

18. The invention as defined in claim 17 wherein said means for relatively rotating said orientation comprises means for mechanically rotating said medium in a direction opposite to fthe angular deection of the beam of said display tube.

19. In a cathode-ray tube display system wherein a data indication is presented on the screen of a cathoderay display tube by brightening the beam of said tube at a controlled time, said beam being deected at a high rate in one dimension and at a relatively low rate in a second dimension, and means are provided for presenting a symbol on said screen adjacent said data indication for identitying said data indication, the combination comprising: a light sensitive device for producing a voltage output in response to light energy, said voltage output being coupled to said cathode-ray display tube to control the brightness of the beam of said tube; a cathode-ray scanner tube having a phosphorescent screen and horizontal and vertical deflection means; a mask comprised of opaque and translucent portions having a pattern representing said symbol, said mask being interposed between the screen of said cathode-ray scanner tube and said light sensitive device; means for rectilinearly sweeping the beam of said cathode-ray scanner tube over said mask, said means including a first generator having a iirst sawtooth voltage output coupled to one of said deflection means, and a second generator having a second sawtooth voltage output coupled to the other of said deliecting means, said second sawtooth voltage output being synchronized with the defiection of the beam of said cathode-ray display tube in one dimension; means for regulating the duration of the sawtooth voltage output of said first generator in inverse proportion to the distance of said data indication from the origin of the sweep in said one dimension over the screen of said cathode-ray display tube; and means for initiating operation of said generators at said controlled time, said second generator being rendered inoperative except for the period of duration of said sav/tooth voltage of said first generator, whreby said beam of said display tube is brightened in accordance with said pattern and said symbol is presented on the screen of said cathode-ray display tube adjacent said indication.

References Cited by the Examiner UNITED STATES PATENTS 2,622,240 12/52 Fleming 343-5 2,935,744 5/60 Foy 343-5 3,017,628 1/62 Landee et al 343-5 CHESTER L. JUSTUS, Primary Examiner.

KATHLEEN CLAFFY, Examiner. 

9. A SAWTOOTH GENERATOR COMPRISING: FIRST AND SECOND TRIODES EACH HAVING A PLATE, A GRID, AND A CATHODE, SAID CATHODES BEING CONNECTED TO A POINT OF REFERENCE POTENTIAL AND EACH OF SAID PLATES BEING CONNECTED TO A SOURCE OF DIRECT VOLTAGE THROUGH A PLATE RESISTOR; A CONNECTION FROM THE PLATE OF SAID FIRST TRIODE TO THE GRID OF SAID SECOND TRIODE THROUGH A FIRST CONDENSER; A CONNECTION FROM THE PLATE OF SAID SECOND TRIODE TO THE GRID OF SAID FIRST TRIODE THROUGH A SECOND CONDENSER; A LEAKAGE PATH FOR SAID FIRST CONDENSER CONNECTED FROM A POINT OF POSITIVE POTENTIAL TO THE JUNCTION OF SAID FIRST CONDENSER AND THE GRID OF SAID SECOND TRIODE; A DIODE CONNECTING THE GRID OF SAID SECOND TRIODE TO SAID POINT OF REFERENCE POTENTIAL, SAID DIODE BEING POLED FOR CONDUCTION FROM THE GRID OF SAID SECOND TRIODE TO SAID POINT OF REFERENCE POTENTIAL, AND A SOURCE OF NEGATIVE CUT-OFF POTENTIAL APPLIED TO THE GRID OF SAID FIRST TRIODE THROUGH A RESISTOR, WHEREBY SAID SECOND TRIODE IS AT MAXIMUM CONDUCTION AND SAID FIRST TRIODE IS CUT OFF; MEANS APPLYING A VOLTAGE PULSE TO THE PLATE OF SAID FIRST TRIODE TO RENDER SAID FIRST TRIODE CONDUCTIVE AT A MAXIMUM LEVEL AND TO CUT OFF SAID SECOND TRIODE; AND MEANS FOR DERIVING A SAWTOOTH OUTPUT VOLTAGE FROM SAID JUNCTION, THE MAGNITUDE OF SAID SAWTOOTH VOLTAGE OUTPUT BEING CONSTANT BETWEEN LIMITS DETERMINED BY THE GRID VOLTAGE OF SAID SECOND TRIODE AT MAXIMUM CONDUCTION AND AT CUT-OFF.
 15. IN A SYSTEM FOR DISPLAYING THE PLAN POSITION OF A MOVING TARGET IN RADIAL AND ANGULAR COORDINATES, SAID SYSTEM INCLUDING A CATHODE-RAY DISPLAY TUBE, THE BEAM OF WHICH IS DEFLECTED RADIALLY AT A RELATIVELY HIGH RATE AS A FUNCTION OF RANGE AND ANGULARLY AT A RELATIVELY SLOW RATE AS A FUNCTION OF AZIMUTH, AND MODULATING MEANS FOR MODULATING SAID BEAM TO PRODUCE A MOVING INDICATION OF THE POSITION OF SAID TARGET IN SAID COORDINATES ON THE SCREEN OF SAID DISPLAY TUBE, THE COMBINATION INCLUDING MEANS FOR SUPERIMPOSING A SYMBOL ON SAID SCREEN CONTINUOUSLY ADJACENT SAID MOVING INDICATION, SAID MEANS FOR SUPERIMPOSING A SYMBOL COMPRISING: A BEAM OF RADIANT ENERGY; A RADIANT ENERGY SENSITIVE DEVICE FOR DEVELOPING AN OUTPUT VOLTAGE IN RESPONSE TO RADIANT ENERGY INTERCEPTED THEREBY, SAID OUTPUT VOLTAGE BEING COUPLED TO SAID MODULATING MEANS FOR FURTHER MODULATING SAID BEAM OF SAID DISPLAY TUBE; A MEDIUM HAVING A RADIATION TRANSMISSION CHARACTERISTIC PATTERN, SAID PATTERN REPRESENTING A SYMBOL, SAID MEDIUM BEING INTERPOSED BETWEEN SAID BEAM OF RADIANT ENERGY AND SAID RADIANT ENERGY SENSITIVE DEVICE; MEANS FOR SCANNING SAID MEDIUM WITH SAID BEAM OF RADIANT ENERGY TO SENSITIZE SAID DEVICE IN ACCORDANCE WITH THE SCANNED PATTERN OF SAID MEDIUM, SAID SCANNING MEANS INCLUDING FIRST AND SECOND GENERATORS FOR GENERATING FIRST AND SECOND DEFLECTION VOLTAGES FOR DEFLECTING SAID BEAM OF RADIANT ENERGY IN FIRST AND SECOND COORDINATES, SAID FIRST GENERATOR BEING SYNCHRONIZED WITH THE RADIAL DEFLECTION OF SAID DISPLAY TUBE; MEANS RESPONSIVE TO COINCIDENCE OF THE BEAM OF SAID DISPLAY TUBE WITH THE ANGULAR POSITIONED COORDINATE OF SAID TARGET INDICATION FOR RENDERING SAID SECOND GENERATOR OPERATIVE FOR GENERATING SAID SECOND DEFLECTION VOLTAGE FOR DEFLECTING SAID BEAM OF RADIANT ENERGY IN SAID SECOND COORDINATE; AND MEANS RESPONSIVE TO THE COINCIDENCE OF THE BEAM OF SAID DISPLAY TUBE WITH THE RADIAL POSITION COORDINATE OF SAID TARGET INDICATION AND TO THE GENERATION OF SAID SECOND DEFLECTION VOLTAGE FOR SUCCESSIVELY RENDERING SAID FIRST GENERATOR OPERATIVE TO SUCCESSIVELY GENERATE SAID FIRST DEFLECTION VOLTAGE FOR DEFLECTING SAID BEAM OF RADIANT ENERGY IN SAID ONE COORDINATE, SAID FIRST GENERATOR BEING INOPERATIVE IN THE ABSENCE OF SAID SECOND DEFLECTION VOLTAGE OUTPUT FROM SAID SECOND GENERATOR, WHEREBY THE BEAM OF SAID DISPLAY TUBE IS MODULATED IN ACCORDANCE WITH SAID PATTERN AND SAID SYMBOL IS SUPERIMPOSED ON SAID DISPLAY TUBE AT A POSITION CONTINUOUSLY ADJACENT SAID TARGET INDICATION. 